1. Field of the Invention
The present invention generally relates to image forming devices, and particularly, to an image forming device such as a dual-sided printer and a duplicator which are capable of both-side printing.
2. Description of the Related Art
FIG. 1 is a schematic diagram showing a conventional dual-sided printer 10 which is capable of both-side printing. The dual-sided printer 10 is comprised of a photoreceptor drum 11, a face-down stacker 12 which is located above the photoreceptor drum 11, a recording medium switchback portion 13 which is located in a side direction of the photoreceptor drum 11, a paper ejection path 14, a paper guide 15, a paper position adjusting mechanism 16, which is located at the end of the paper guide 15, and a paper cartridge 17. The face-down stacker 12 is capable of storing printed papers with a latest printed surface facing downward, i.e., the stacker 12 is capable of storing the printed papers in order of page numbers without requiring a large memory. The recording medium switchback portion 13 functions as a transfer means which receives a paper, one surface (upper surface) of which is printed by passing the photoreceptor drum 11, and transfers the paper in the reversed direction in order to perform a printing of the other side of the paper. Also, the paper guide 15 is operated so as to guide a paper, which is fed from the recording medium switchback portion 13, to an inlet of the photoreceptor drum 11.
In the dual-sided printer 10, the both-side printing is carried out as follows. When a paper is fed from the paper cartridge 17 in the direction A shown in FIG. 1, it is passed underneath the photoreceptor drum 11 as indicated by the arrow B and its upper surface is printed. Then, the paper is transferred in the direction C and reaches the recording medium switchback portion 13. At the recording medium switchback portion 13, the direction of the paper transfer is reversed and it is fed in the direction indicated by the arrows D and E towards the paper position adjusting mechanism 16 (the movement of a paper from the paper cartridge 17 to the paper position adjusting mechanism 16 is hereinafter referred to as a first run of the paper). The position of the paper which may be shifted during the first run may be adjusted (by centering or skew correction) by the paper position adjusting mechanism 16. After this, the paper is transferred in the direction indicated by the arrow F and passed again underneath the photoreceptor drum 11 so that the other side of the paper is printed. The paper, both sides of which are printed, is then moved in the direction indicated by the arrow G and is stored on the face-down stacker 12 (the movement of a paper from the paper position adjusting mechanism 16 to the face-down stacker 12 is hereinafter referred to as a second run of the paper).
However, in the conventional dual-sided printer 10, the operation of the paper position adjusting mechanism 16 is started when a paper is transferred to the end of the paper guide 15 and the transfer of the paper is stopped.
Thus, since the operation of the paper position adjusting mechanism 16 is started after the transfer of the paper is stopped, the actual operation of the dual-sided printer 10 during the termination of the first run of a paper and the start of the second run of the paper may become as indicated in FIG. 2, i.e., paper transfer (first run).fwdarw.paper transfer stop.fwdarw.paper position adjustment.fwdarw.paper transfer (second run). Thus, a time for adjusting the position of a paper is additionally required besides a time for transferring the paper, and hence the speed of the both-side printing is slowed down.
Also, the paper position adjusting mechanism 16 has a structure in which a pair of right and left guiding members are moved symmetrically towards the center so as to push a paper by one of the guiding members, which is provided with an elastic member, and receives the paper by the other guiding member. In this manner, the position of the paper may be corrected.
However, when the pair of right and left guiding members are separated from the paper, since both of them move symmetrically, the paper is still pushed by the elastic member due to its force as it returns to the original position, and hence there is a problem that the position of the paper may be shifted again.